The present invention relates generally to retrievable well packers for sealing a tubing string, for example, to a surrounding well conduit such as is provided by a casing or well liner, and, specifically, to a holding mechanism for preventing premature release of the packer from sealing and anchoring engagement in the well conduit.
Well packers are shown in the prior art which are set by manipulation of a tubing string from which the tools are suspended, or by application of hydraulic pressure by means of the tubing string to the tool. Anchoring devices used with such tools commonly include a plurality of slip members with opposed camming surfaces which cooperate with complimentary opposed frusto-conical wedging surfaces, whereby the slip members are extended radially into gripping engagement with the well conduit in response to relative axial movement of the wedging surfaces. Sealing devices are known which include annular resilient seal members which expand radially into sealing engagement with the well conduit as the sealing members are axially compressed by the setting mechanism of the tool. The packers are set, rendering the sealing mechanism and the anchoring mechanism in appropriate engagement with the surrounding well conduit in response to relative longitudinal movement of the various packer components, effected either hydraulically or mechanically.
It is critical that the well packer remain locked in its set configuration in spite of variation of well pressures and temperatures and/or manipulation of the tubing string. Various prior packer designs allow the packer to be retrieved from the well bore by appropriate manipulation of the tubing string. In some instances, the packer was released from its set configuration by a straight pull upwardly on the tubing string. Because premature release could result from unwanted longitudinal movement of the tubing string in such designs, pressure-responsive clamping or holding devices were utilized to prevent unwanted movement. Such longitudinal tubing string movement could occur, for example, in response to a variation in tubing string length due to temperature variations, or an increase in down-hole fluid pressure acting upwardly on the tubing string.
There exists a need, therefore, for a retrievable well packer employing pressure responsive clamping or holding devices for preventing unwanted longitudinal movement of the packer components and tubing string which might otherwise release the packer prematurely.
There exists a need for such a retrievable packer featuring a clamping or holding device which is resistant to both an increase in down-hole fluid pressure acting upwardly on the tubing string and to the variation in tubing string length due to temperature variations.
There exists a need for such a packer which can conveniently be released by increasing the annulus pressure above a predetermined reference index point to thereby release the holding device to allow the packer to be retrieved by a straight pull on the tubing string.